We have learnt that a computer has many components and attachments
that perform specific functions and enable us to use it for different purposes
like solving sums, typing documents, searching for information, playing games,
listening to music and so on. We also know that a computer remembers the
information saved in it.
Some common components of computer are keyboard, monitor, mouse,
printer, etc. These components must be connected to the CPU, which is the most
important-the
brain of the computer
All these parts are together called the hardware or computer
peripherals. You would recall that the computer hardware can be broadly
categorized into the following types:
Input Devices
• Output Devices
• Processing Unit
• Storage Devices
You are already familiar with different types of input and output
devices, and the Central Processing Unit. Let us now learn about storage
devices of a computer.
STORAGE DEVICES
Devices in which a computer stores data, instructions and
information are called storage devices. As the stored data can be accessed by
the computer any time, these storage devices serve as the memory of the
computer. The storage capacity of a computer is determined by the amount of
data it can save in its memory.
➤ Unit of
measurement of computer memory
The only language that a computer understands is binary language.
Binary means 'two'. The Binary language consists of two digits, O and 1. The
computer understands only two digits, O and 1. Therefore, in order to store or
process data, the computer first converts it into a combination of these two
digits.
The smallest amount of data or information that a computer can
store is called bit. The term 'bit' comes from two words-binary and digit.
Space taken by each digit is called 1 bit of information. 8 bits make up a byte
(B). The computer memory is represented in bytes. In other words, byte is the
basic unit of measurement of computer memory. These days, the storage capacity
of computer is measured in much bigger units such as Megabytes (MB), Gigabytes
(GB) and Terabytes (TB).
1 bit (binary digit) = 0 or 1
4 bits 1 nibble
8 bits = 1 byte (B)
1024 B 1 kilobyte (KB)
1024 KB 1 megabyte (MB)
1024 MB = 1 gigabyte (GB)
1024 GB = 1 terabyte (TB)
COMPUTER MEMORY AND ITS TYPES
There are two types of computer memory: primary memory and
secondary memory.
➤ Primary
Memory
It is the memory that the computer uses for its internal
functions. A computer will not be able to run without this memory. Thus, it is
also called the internal memory or main memory of the computer. It can be
further divided into two parts, RAM (Random Access Memory) and ROM (Read Only
Memory). These are fitted as chips on the motherboard. They can be directly
accessed by the CPU.
Random Access Memory (RAM)
When a computer starts, the operating system is loaded onto the
RAM. When you are working on a program, it is actually loaded on the RAM. RAM
saves your work on the computer while the computer is running and you are
working on it. The moment you switch off the system, the data from this memory
gets erased. This means that RAM stores the data and instructions which are in
current use only. Hence, it is called the temporary memory or vo computer. If
you want to store your work permanently in the computer memory, you must save
it before switching off the computer. You can read the information loaded on
the RAM as well as write on it. Therefore, it is also called read/write memory.
of the
RAM greatly controls the performance of a computer. The greater
the RAM installed in a computer, the greater the number and size of programs
that can be run on the computer simultaneously. A computer system can have RAM
of different capacities like 128 MB, 256 MB, 512 MB or more. More RAM can also
be added to the existing system to improve its performance.
Read Only Memory (ROM)
ROM is that part of the computer memory which comprises of
instructions put by the manufacturer to run the computer. ROM stores a special
software called BIOS (Basic Input/ Output System) which helps to load the
operating system when a computer is switched on. These instructions permanently
stay in the computer memory even when the computer is switched off. This memory
is therefore called the permanent memory or non-volatile memory. ROM is the
memory from which data can only be read. It is not possible to overwrite or
save any data in this memory unit.
ROM
➤ Secondary
Memory Data storage devices Primary memory has limited capacity and/or is
volatile. Hence, to save and store our work and data even when the computer is
switched off, we need secondary memory. These are data storage devices that are
either fitted inside the CPU box (for example, the hard disk) or are attached
externally (for example, CD, DVD and pen drive). As the secondary storage
devices provide additional storage they are also called auxiliary storage
devices. The storage capacity of secondary or external memory is much greater
than the internal memory.
Hard Disk
A hard disk is a part of a unit called hard disk drive that is
fitted inside the CPU cabinet. When we press 'save' button while working on the
computer, our work is saved in the hard disk of the computer. The hard disk is
a magnetic disk with a huge storage capacity that enables us to save all our
files, folders, music, pictures, videos and other data securely in the
computer. It can have a storage capacity of up to 1 TB. These days, we can also
attach additional hard disks externally to our computer in order
to save additional data or to take the back up of precious files.
Let us now learn about some more secondary storage devices that
not only help us save our work on them but also enable us to easily share or
transfer it from one computer to the other.
Compact Disc (CD)
You must have seen or used this round disc with a shiny surface.
It can store up to 700 MB of data. A CD can either be a CD-ROM (Read-Only
Compact Disc), CD-R (Recordable Compact Disc) or CD-RW (Re-writable Compact
Disc).
CD
Digital Video Disk or Digital Versatile Disk (DVD)
A DVD looks similar to a CD but can hold data upto 4.7 GB which is
much more than a CD can hold. It not only holds a larger amount of data, but
its audio and video quality is also much superior.
Blu-Ray disc (BD)
DVD
BD
A blu-ray disc also appears like a CD or DVD as it has the same
shape, size and thickness. But it is also very different from them. The grooves
on a blu-ray disc are placed much closer. About 25 GB of data can be stored in
a single layer blu-ray disc. It is named so because blue laser is used to read
this disc and hence, it can only run on a blu-ray player. Though a blu-ray disc
cannot run in a DVD player, you can run your CDs and DVDs in a Blu-ray player.
Flash drive (or Pen Drive)
A flash drive, also known as a pen drive or USB drive, is a very
small storage device that can be easily carried anywhere in your pocket. This
does not need any special drive or player to run. It can be directly inserted
into the USB port of the computer to run or to transfer data. Flash drives are
available with storage capacity as little as 256 MB and as large as 1 TB. This
means that you can easily transfer a huge amount of data using a flash drive.
It takes very little space and does not require careful handling as in the case
of CDs, DVDs and BDs. It can be formatted again and again for multiple usage.
The Right Way
Before buying a storage device, determine the size of the data
that you want to store in it. Calculate the cost per MB of data for each device
you are considering. Do not buy a secondary storage device having a large
capacity just to show off because the larger the capacity, the more price you
have to pay.
Let Us Recall
A computer has many components and attachments that perform
specific functions. All these parts together are called hardware or computer
peripherals.
The hardware of computer can be categorized as input devices,
processing unit, output devices and storage devices.
Devices in which a computer stores data, instructions and
information are called storage devices. Storage devices serve as the memory of
the computer.
There are two types of computer memory: primary memory and
secondary memory.
Primary memory are storage devices without which a computer cannot
run. They are further divided into two types: RAM and ROM.
Secondary memory comprises storage devices that are either fitted
in the computer (e.g., hard disk) or attached externally (e.g., CD, DVD, BD and
Pen drive).
Exercises
A. Tick() the correct option.
This is not a storage device.
(a) Keyboard
The moment the system is switched off, the data from this memory
is lost.
(c) RAM
This part of computer memory comprises of permanent instructions
to run the computer.
(b) ROM
This storage device can be directly inserted into the USB port of
the computer.
(b) Flash Drive
It uses blue laser to read data.
(b) BD
B. Match the following:
Smallest unit of data which comes from the two words 'binary' and
'digit'
(c) Bit
1024 megabytes
(f) 1 GB
Short for digital versatile disc
(d) DVD
Can store data of up to 25 GB
(e) Blu-ray
A set of 8 bits
(a) Byte
Also known as pen drive
(b) Flash drive
C. Complete the following table.
|
Unit |
Equivalent |
|
4 bits |
1 nibble |
|
8 bits |
1 byte (B) |
|
1024 B |
1 kilobyte (KB) |
|
1024 KB |
1 megabyte (MB) |
|
1024 MB |
1 gigabyte (GB) |
D. Fill in the blanks.
1.
Auxiliary storage devices are also called secondary storage
devices.
2.
Compact Disc (CD) is the storage disc that can hold about 700
MB of data.
3.
ROM comprises of instructions to run the computer.
4.
A blu-ray disc runs only on a blu-ray player.
5.
A DVD can hold up to 4.7 GB data.
6.
Our work is saved into the hard disk of the computer.
E. Distinguish between:
1. Primary memory and secondary memory
|
Feature |
Primary Memory |
Secondary Memory |
|
Role |
Main memory for active programs and data |
Long-term storage for files and programs |
|
Speed |
Faster |
Slower |
|
Access |
Direct by CPU |
Indirect, data transferred to primary memory
first |
|
Volatility |
Volatile (data lost when power off) |
Non-volatile (data retained when power off) |
|
Capacity |
Smaller |
Larger |
|
Examples |
RAM, ROM |
Hard disk, SSD, CD, DVD, USB |
2. RAM and ROM
|
Feature |
RAM (Random Access Memory) |
ROM (Read Only Memory) |
|
Role |
Temporary storage for active data and programs |
Permanent storage for essential system
instructions |
|
Read/Write |
Read and write |
Read only |
|
Volatility |
Volatile |
Non-volatile |
|
Feature |
RAM (Random Access Memory) |
Slower |
3. DVD and BD
|
Feature |
DVD (Digital Versatile Disc) |
BD (Blu-ray Disc) |
|
Feature |
Up to 17 GB |
Up to 100 GB |
|
Feature |
Lower |
Higher |
|
Feature |
Red laser |
Blue-violet laser |
|
Feature |
Good |
Excellent |
|
Feature |
Similar to CD |
Similar to CD |
F. Arrange these amounts of data in increasing order of size.
900 KB (0.89 MB)
499 MB
Half a GB (512 MB)
600 GB (614400 MB)
1 TB (1048576 MB)
G. Answer the following questions.
Why is primary memory also called the main
memory?
Primary memory is
also called the main memory because it is essential for the computer's
operation.
Name any four secondary storage devices of
a computer.
Hard disk, SSD, CD,
and USB drive are four secondary storage devices.
What is Binary language?
Binary language is
a number system using only two digits, 0 and 1.
Mention any two differences between a CD
and a DVD.
A CD has a lower
storage capacity and uses a red laser compared to a DVD's higher capacity and
red laser.
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